I'm sure my group is sick of hearing me harp about this, but I thought I should get this on the radar for something to be addressed in an update. Here's an illustration of the size issue with HotA.
Lets say you have 3 universal wizards: a tiny grig, medium human, and huge titan. They each have a 3 lb medium club, and are all proficient in the weapon. The grig and titan can't use the medium club in melee because it is too big/small.
Now the grig casts enlarge person and the titan casts reduce person. The small grig can use a medium club two handed, and the large titan can use a medium club as a light weapon. In both cases, the club is the wrong size, and there is a -2 penalty for melee attacks.
The question is, in which cases can the caster above use HotA with a medium club, and at what penalty?
If you interpret HotA as an extension of the caster and only allow the spell to work with one handed weapons, then:
medium human: no penalty
tiny grig and huge titan: cannot use weapon
small grig: cannot use weapon
large titan: can use weapon at -2 penalty
The part that is unsettling to me is that in all cases, the weapon and the spell strength are the same. The spell effect is independent of caster size and STR. It's simply telekinesis of a non-magical object up to 5 pounds. Furthermore, the caster is not actually wielding the weapon. It's being manipulated magically.
There are a few ways to make this more internally consistent:
1) HotA creates a medium sized hand that can wield light or one-handed medium weapons. Large light weapons and small one- and two-handed weapons can be used at a -2 penalty. In this case, the human, grig, and titan can use the medium club w/o penalty regardless of size. The 5 pound limit could be retained. Small spellcasters would be forced to carry a medium weapon if they wanted to avoid the -2 penalty though, which is bad.
2) HotA works with any weapon up to 5 pounds. Caster size is irrelevant. The weapon category is based on the size of the wielder and there is no wielder. This means you can use a medium mithral greatsword as a medium human. If you are not proficient, you take a -4 penalty. This opens the door to serious abuse (Gargantuan mithral siangham???).
3) HotA creates a hand of the size of the caster, which can wield light or one-handed weapons of that size, with no weight restrictions. Smaller/larger weapons can be used at a -2 penalty if they are not two-handed for that size. Now a titan can wield heavier weapons, and a grig will wield lighter weapons. The spell strength adjusts based on the caster size. In this way, all casters can use their normal weapons effectively.
I think #3 most closely matches the spirit of the ability, and makes it so it is usable by any creature, regardless of size. To me, the intent is to give a wizard a ranged attack option relative to the weapon they carry.